Forming multiple aerial images in a single lithography exposure pass

ABSTRACT

A set of the pulses of light in a light beam is passed through a mask toward a wafer during a single exposure pass; at least a first aerial image and a second aerial image on the wafer based on pulses of light in the set of pulses that pass through the mask is generated during a single exposure pass, the first aerial image is at a first plane on the wafer and the second aerial image is at a second plane on the wafer, the first plane and the second plane being spatially distinct from each other and separated from each other by a separation distance along the direction of propagation; and a three-dimensional semiconductor component is formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/755,993, which is the national phase of International Application No.PCT/US2018/052949, filed Sep. 26, 2018 and titled FORMING MULTIPLEAERIAL IMAGES IN A SINGLE LITHOGRAPHY EXPOSURE PASS, which claimspriority to U.S. Application No. 62/574,628, which was filed on Oct. 19,2017. Each of these patent applications is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

This disclosure relates to forming multiple aerial images in a singlelithography exposure pass. The techniques discussed below may be used,for example, to form a three-dimensional semiconductor component.

BACKGROUND

Photolithography is the process by which semiconductor circuitry ispatterned on a substrate such as a silicon wafer. A photolithographyoptical source provides the deep ultraviolet (DUV) light used to exposea photoresist on the wafer. DUV light for photolithography is generatedby excimer optical sources. Often, the optical source is a laser sourceand the pulsed light beam is a pulsed laser beam. The light beam ispassed through a beam delivery unit, a reticle or a mask, and thenprojected onto a prepared silicon wafer. In this way, a chip design ispatterned onto a photoresist that is then etched and cleaned, and thenthe process repeats.

SUMMARY

In one general aspect, a method of forming a three-dimensionalsemiconductor component using a photolithography system includesdirecting a pulsed light beam along a direction of propagation toward amask, the pulsed light beam including a plurality of pulses of light;passing a set of the pulses of light in the light beam through the masktoward a wafer during a single exposure pass; generating, during thesingle exposure pass, at least a first aerial image and a second aerialimage on the wafer based on pulses of light in the set of pulses thatpass through the mask, the first aerial image being at a first plane onthe wafer and the second aerial image being at a second plane on thewafer, the first plane and the second plane being spatially distinctfrom each other and separated from each other by a separation distancealong the direction of propagation; and forming the three-dimensionalsemiconductor component based on an interaction between light in thefirst aerial image and a material in a first portion of the wafer and aninteraction between light in the second aerial image and a material in asecond portion of the wafer. At least one of the pulses in the set ofpulses has a first primary wavelength and at least one of the otherpulses in the set of pulses has a second primary wavelength that isdifferent from the first primary wavelength, such that the separationdistance is formed during the single exposure pass based on thedifference between the first primary wavelength and the second primarywavelength.

Implementations may include one or more of the following features. Atleast one of the pulses in the set of pulses that passes through themask during the single exposure pass may have more than one primarywavelength of light.

Each primary wavelength may be separated by a spectral separation of 200femtometers (fm) to 500 picometers (pm) from the nearest other primarywavelength.

The separation distance between the first aerial image and the secondaerial image may change during the single exposure pass.

The single exposure pass may be a first exposure pass, and the methodalso may include passing a second set of pulses of light in the lightbeam through the mask toward the wafer during a second exposure pass andafter the first exposure pass is completed. The separation distancebetween the first aerial image and the second aerial image is differentduring the first exposure pass and the second exposure pass.

The separation distance between the first aerial image and the secondaerial image may be set prior to the single exposure pass, and, in someimplementations, the separation distance does not change during thesingle exposure pass. The separation distance between the first aerialimage and the second aerial image may be set to accommodate one or morefeatures of the photolithography system.

The set of pulses may include a first group of pulses of light and asecond group of pulses of light, each pulse in the first group of pulsesof light has the first primary wavelength, each pulse in the secondgroup of pulses may have the second primary wavelength, and the methodalso may include: controlling a property of the first group of pulses tothereby control an amount of light in the first aerial image; andcontrolling a property of the second group of pulses to thereby controlan amount of light in the second aerial image. The property of the firstgroup may be a count of pulses in the first group, and the property ofthe second group may be a count of pulses in the second group.Controlling the count of pulses in the first group may includedetermining, before the single exposure pass begins, a first number ofpulses to include in the first group of pulses, and controlling thesecond number of pulses may include determining, before the singleexposure pass, a second number of pulses to include in the second groupof pulses. The first group of pulses and the second group of pulses mayinclude all of the pulses that pass through the mask in the singleexposure pass. Determining the first number of pulses and the secondnumber of pulses may include one or more of: (a) receiving input from anoperator and (b) accessing a pre-defined setting associated with thephotolithography system. The property of the first group of pulses mayinclude an intensity of each pulse in the first group, and the propertyof the second group of pulses may include an intensity of each pulse inthe second group.

The first plane on the wafer and the second plane on the wafer may beplanes that are substantially perpendicular to the direction ofpropagation.

In some implementations, a first feature of the three-dimensionalsemiconductor is formed at the first plane, a second feature of thethree-dimensional semiconductor is formed at the second plane, and thefirst and second features are displaced from each other by a sidewallthat extends substantially parallel to the direction of propagation.

The three-dimensional semiconductor component may be a three-dimensionalNAND flash memory component.

The first plane may correspond to a first focal plane and the secondplane corresponds to a second focal plane, and the separation distancebetween the first plane and the second plane is based on a differencebetween one or more wavelengths in a pulse of light that passes throughthe mask or a difference between a wavelengths among discrete pulses inthe set of pulses.

In another general aspect, a photolithography system includes a lightsource; a lithography scanner apparatus including: a mask positioned tointeract with a pulsed light beam from the light source, and a waferholder; and a control system coupled to the light source, the controlsystem configured to cause the light source to emit the pulsed lightbeam toward the lithography scanner apparatus during a single exposurepass such that, during the single exposure pass, at least a first aerialimage and a second aerial image are formed on a wafer received at thewafer holder based on pulses of light in a set of pulses of light thatpass through the mask along a direction of propagation, the first aerialimage being at a first plane on the wafer and the second aerial imagebeing at a second plane on the wafer, the first plane and the secondplane being spatially distinct from each other and separated from eachother by a separation distance along the direction of propagation, and athree-dimensional semiconductor component is formed based on aninteraction between light in the first aerial image and a material in afirst portion of the wafer and an interaction between light in thesecond aerial image and a material in a second portion of the wafer. Atleast one of the pulses in the set of pulses has a first primarywavelength, at least one of the other pulses in the set of pulses has asecond primary wavelength that is different from the first primarywavelength, and the separation distance between first aerial image andthe second aerial image is based on the difference between the firstprimary wavelength and the second primary wavelength.

Implementations may include one or more of the following features. Thecontrol system may include a computer-readable storage medium, one ormore electronic processors coupled to the computer-readable storagemedium, and an input/output interface, and a recipe related to thephotolithography system is stored on the computer-readable storagemedium. The recipe may specify the separation distance. The recipespecifies the separation distance on a per-wafer or per-lot basis. Thelight source may include a krypton fluoride (KrF) gain medium or a argonfluoride (ArF) gain medium.

Implementations of any of the techniques described above and herein mayinclude a process, an apparatus, a control system, instructions storedon a non-transient machine-readable computer medium, and/or a method.The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an example of an implementation of aphotolithography system.

FIG. 1B is a block diagram of an example of an implementation of anoptical system for the photolithography system of FIG. 1A.

FIG. 1C is a cross-sectional view of an example of a wafer exposed bythe photolithography system of FIG. 1A.

FIG. 2A is a block diagram of another example of an implementation of aphotolithography system.

FIG. 2B is a block diagram of an example of an implementation of aspectral feature selection module that may be used in a photolithographysystem.

FIG. 2C is a block diagram of an example of an implementation of a linenarrowing module.

FIGS. 3A-3C are plots of data that relate to the production of pulsesand/or bursts of pulses in an optical source, in which FIG. 3C shows anamplitude of a trigger signal as a function of time.

FIG. 4 is a block diagram of another example of an implementation of aphotolithography system.

FIG. 5 is a flow chart of an example of a process for forming athree-dimensional semiconductor component.

FIGS. 6A and 6B each show an example of an optical spectrum of a singlepulse of light.

FIG. 7 shows an example of an average optical spectrum for a singleexposure pass.

FIGS. 8A and 8B show side and top cross-sectional views, respectively,of an example of a wafer.

FIGS. 9A and 9B show side and top cross-sectional views, respectively,of an example of a three-dimensional semiconductor component.

FIGS. 10A and 10B show examples of simulated data.

DETAILED DESCRIPTION

Techniques for forming more than one aerial image, each at a differentplane, in a single lithography pass, and forming a three-dimensionalsemiconductor component using the aerial images are discussed herein.

Referring to FIG. 1A, a photolithography system 100 includes an optical(or light) source 105 that provides a light beam 160 to a lithographyexposure apparatus 169, which processes a wafer 170 received by a waferholder or stage 171. The light beam 160 is a pulsed light beam thatincludes pulses of light separated from each other in time. Thelithography exposure apparatus 169 includes a projection optical system175 through which the light beam 160 passes prior to reaching the wafer170, and a metrology system 172. The metrology system 172 may include,for example, a camera or other device that is able to capture an imageof the wafer 170 and/or the light beam 160 at the wafer 170, or anoptical detector that is able to capture data that describescharacteristics of the light beam 160, such as intensity of the lightbeam 160 at the wafer 170 in the x-y plane. The lithography exposureapparatus 169 can be a liquid immersion system or a dry system. Thephotolithography system 100 also may include a control system 150 tocontrol the light source 105 and/or the lithography exposure apparatus169.

Microelectronic features are formed on the wafer 170 by, for example,exposing a layer of radiation-sensitive photoresist material on thewafer 170 with the light beam 160. Referring also to FIG. 1B, theprojection optical system 175 includes a slit 176, a mask 174, and aprojection objective, which includes a lens 177. The light beam 160enters the optical system 175 and impinges on the slit 176, and at leastsome of the beam 160 passes through the slit 176. In the example ofFIGS. 1A and 1B, the slit 176 is rectangular and shapes the light beam160 into an elongated rectangular shaped light beam. A pattern is formedon the mask 174, and the pattern determines which portions of the shapedlight beam are transmitted by the mask 174 and which are blocked by themask 174. The design of the pattern is determined by the specificmicroelectronic circuit design that is to be formed on the wafer 170.

The shaped light beam interacts with the mask 174. The portions of theshaped light beam that are transmitted by the mask 174 pass through (andmay be focused by) the projection lens 177 and expose the wafer 170. Theportions of the shaped light beam that are transmitted by the mask 174form an aerial image in the x-y plane in the wafer 170. The aerial imageis the intensity pattern formed by the light that reaches the wafer 170after interacting with the mask 174. The aerial image is at the wafer170 and extends generally in the x-y plane.

The system 100 is able to form a plurality of aerial images during asingle exposure pass, with each of the aerial images being at aspatially distinct location along the z axis in the wafer 170. Referringalso to FIG. 1C, which shows a cross-sectional view of the wafer 170 inthe y-z plane, the projection optical system 175 forms two aerial images173 a, 173 b at different planes along the z axis in a single exposurepass. As discussed in greater detail below, each of the aerial images173 a, 173 b is formed from light having a different primary wavelength.

The location of the aerial image along the z axis depends on thecharacteristics of the optical system 175 (including the projection lens177 and the mask 174) and the wavelength of the light beam 160. Thefocal position of the lens 177 depends on the wavelength of the lightincident on the lens 177. Thus, varying or otherwise controlling thewavelength of the light beam 160 allows the position of the aerial imageto be controlled. By providing pulses having different primarywavelengths of light during a single exposure pass, a plurality (two ormore) of aerial images, which are each at a different location along thez axis, may be formed in a single exposure pass without moving theoptical system 175 (or any components of the optical system 175) and thewafer 170 relative to each other along the z axis.

In the example of FIG. 1A, light passing through the mask 174 is focusedto a focal plane by the projection lens 177. The focal plane of theprojection lens 177 is between the projection lens 177 and the waferstage 171, with the position of the focal plane along the z axisdepending on the properties of the optical system 175 and the wavelengthof the light beam 160. The aerial images 173 a, 173 b are formed fromlight having different wavelengths, thus the aerial images 173 a, 173 bare at different locations in the wafer 170. The aerial images 173 a,173 b are separated from each other along the z axis by a separationdistance 179. The separation distance 179 depends on the differencebetween the wavelength of the light that forms the aerial image 173 aand the wavelength of the light that forms the aerial image 173 b.

The wafer stage 171 and the mask 174 (or other parts of the opticalsystem 175) generally move relative to each other in the x, y, and zdirections during scanning for routine performance corrections andoperation, for example, the motion may be used to accomplish basicleveling, compensation of lens distortions, and for compensation ofstage positioning error. This relative motion is referred to asincidental operational motion. However, in the system of FIG. 1A, therelative motion of the wafer stage 171 and the optical system 175 is notrelied upon to form the separation distance 179. Instead, the separationdistance 179 is formed due to the ability to control the primarywavelengths in the pulses that pass through the mask 174 during theexposure pass. Thus, unlike some prior systems, the separation distance179 is not created only by moving the optical system 175 and the wafer170 relative to each other along the z direction. Moreover, the aerialimages 173 a and 173 b are both present at the wafer 170 during the sameexposure pass. In other words, the system 100 does not require that theaerial image 173 a be formed in a first exposure pass and the aerialimage 173 b be formed in a second, subsequent exposure pass.

The light in the first aerial image 173 a interacts with the wafer at aportion 178 a, and the light in the second aerial image 173 b interactswith the wafer at a portion 178 b. These interactions may formelectronic features or other physical characteristics, such as openingsor holes, on the wafer 170. Because the aerial images 173 a, 173 b areat different planes along the z axis, the aerial images 173 a, 173 b maybe used to form three-dimensional features on the wafer 170. Forexample, the aerial image 173 a may be used to form a periphery region,and the aerial image 173 b may be used to form a channel, trench, orrecess that is at a different location along the z axis. As such, thetechniques discussed herein may be used to form a three-dimensionalsemiconductor component, such as a three-dimensional NAND flash memorycomponent.

Before discussing additional details related to forming multiple aerialimages in a single exposure pass, example implementations of the lightsource 105 and the photolithography system 100 are discussed withrespect to FIGS. 2A-2C, 3A-3C, and 4 .

Referring to FIG. 2A, a block diagram of a photolithography system 200is shown. The system 200 is an example of an implementation of thesystem 100 (FIG. 1A). For example, in the photolithography system 200,an optical source 205 is used as the optical source 105 (FIG. 1A). Theoptical source 205 produces a pulsed light beam 260, which is providedto the lithography exposure apparatus 169. The optical source 205 maybe, for example, an excimer optical source that outputs the pulsed lightbeam 260 (which may be a laser beam). As the pulsed light beam 260enters the lithography exposure apparatus 169, it is directed throughthe projection optical system 175 and projected onto the wafer 170. Inthis way, one or more microelectronic features are patterned onto aphotoresist on the wafer 170 that is then developed and cleaned prior tosubsequent process steps, and the process repeats. The photolithographysystem 200 also includes the control system 250, which, in the exampleof FIG. 2A, is connected to components of the optical source 205 as wellas to the lithography exposure apparatus 169 to control variousoperations of the system 200. The control system 250 is an example of animplementation of the control system 250 of FIG. 1A.

In the example shown in FIG. 2A, the optical source 205 is a two-stagelaser system that includes a master oscillator (MO) 212 that provides aseed light beam 224 to a power amplifier (PA) 230. The MO 212 and the PA230 may be considered to be subsystems of the optical source 205 orsystems that are part of the optical source 205. The power amplifier 230receives the seed light beam 224 from the master oscillator 212 andamplifies the seed light beam 224 to generate the light beam 260 for usein the lithography exposure apparatus 169. For example, the masteroscillator 212 may emit a pulsed seed light beam, with seed pulseenergies of approximately 1 milliJoule (mJ) per pulse, and these seedpulses may be amplified by the power amplifier 230 to about 10 to 15 mJ.

The master oscillator 212 includes a discharge chamber 240 having twoelongated electrodes 217, a gain medium 219 that is a gas mixture, and afan for circulating gas between the electrodes 217. A resonator isformed between a line narrowing module 216 on one side of the dischargechamber 240 and an output coupler 218 on a second side of the dischargechamber 240. The line narrowing module 216 may include a diffractiveoptic such as a grating that finely tunes the spectral output of thedischarge chamber 240. FIGS. 2B and 2C provide additional detail aboutthe line narrowing module 216.

FIG. 2B is a block diagram of an example of an implementation of aspectral feature selection module 258 that includes one or moreinstances of the line narrowing module 216. The spectral featureselection module 258 couples to light that propagates in the opticalsource 205. In some implementations (such as shown in FIG. 2B), thespectral feature selection module 258 receives the light from thechamber 214 of the master oscillator 212 to enable the fine tuning ofthe spectral features such as wavelength and bandwidth within the masteroscillator 212.

The spectral feature selection module 258 may include a control modulesuch as a spectral feature control module 254 that includes electronicsin the form of any combination of firmware and software. The controlmodule 254 is connected to one or more actuation systems such asspectral feature actuation systems 255_1 to 255_n. Each of the actuationsystems 255_1 to 255_n may include one or more actuators that areconnected to respective optical features 256_1 to 256_n of an opticalsystem 257. The optical features 256_1 to 256_n are configured to adjustparticular characteristics of the generated light beam 260 to therebyadjust the spectral feature of the light beam 260. The control module254 receives a control signal from the control system 250, the controlsignal including specific commands to operate or control one or more ofthe actuation systems 255_1 to 255_n. The actuation systems 255_1 to255_n can be selected and designed to work together, that is, in tandem,or the actuation system 255_1 to 255_n may be configured to workindividually. Moreover, each actuation system 255_1 to 255_n may beoptimized to respond to a particular class of disturbances.

Each optical feature 256_1 to 256_n is optically coupled to the lightbeam 260 produced by the optical source 105. The optical system 257 maybe implemented as a line narrowing module 216C such as that shown inFIG. 2C. The line narrowing module includes as the optical features256_1 to 256_n dispersive optical elements such as a reflective gratings291 and refractive optical elements such as prisms 292, 293, 294, 295.One or more of the prisms 292, 293, 294, 295 may be rotatable. Anexample of this line narrowing module can be found in U.S. applicationSer. No. 12/605,306, titled SYSTEM METHOD AN APPARATUS FOR SELECTING ANDCONTROLLING LIGHT SOURCE BANDWIDTH and filed on Oct. 23, 2009 (the '306application). In the '306 application, a line narrowing module isdescribed that includes a beam expander (including the one or moreprisms 292, 293, 294, 295) and the dispersive element such as thegrating 291. The respective actuation systems for the actuatable opticalfeatures such as the grating 291, and one or more of the prisms 292,293, 294, 295 are not shown in FIG. 2C.

Each of the actuators of the actuation systems 255_1 to 255_n is amechanical device for moving or controlling the respective opticalfeatures 256_1 to 256_n of the optical system 257. The actuators receiveenergy from the module 254, and convert that energy into some kind ofmotion imparted to the optical features 256_1 to 256_n of the opticalsystem 257. For example, in the '306 application, actuation systems aredescribed such as force devices (to apply forces to regions of thegrating) and rotation stages for rotating one or more of the prisms ofthe beam expander. The actuation systems 255_1 to 255_n may include, forexample, motors such as stepper motors, valves, pressure-controlleddevices, piezoelectric devices, linear motors, hydraulic actuators,and/or voice coils.

Returning to FIG. 2A, the master oscillator 212 also includes a linecenter analysis module 220 that receives an output light beam from theoutput coupler 218 and a beam coupling optical system 222 that modifiesthe size or shape of the output light beam as needed to form the seedlight beam 224. The line center analysis module 220 is a measurementsystem that may be used to measure or monitor the wavelength of the seedlight beam 224. The line center analysis module 220 may be placed atother locations in the optical source 205, or it may be placed at theoutput of the optical source 205.

The gas mixture used in the discharge chamber 240 may be any gassuitable for producing a light beam at the wavelength and bandwidthrequired for the application. For an excimer source, the gas mixture maycontain a noble gas (rare gas) such as, for example, argon or krypton, ahalogen, such as, for example, fluorine or chlorine and traces of xenonapart from helium and/or neon as buffer gas. Specific examples of thegas mixture include argon fluoride (ArF), which emits light at awavelength of about 193 nm, krypton fluoride (KrF), which emits light ata wavelength of about 248 nm, or xenon chloride (XeCl), which emitslight at a wavelength of about 351 nm. The excimer gain medium (the gasmixture) is pumped with short (for example, nanosecond) current pulsesin a high-voltage electric discharge by application of a voltage to theelongated electrodes 217.

The power amplifier 230 includes a beam coupling optical system 232 thatreceives the seed light beam 224 from the master oscillator 212 anddirects the light beam through a discharge chamber 240, and to a beamturning optical element 248, which modifies or changes the direction ofthe seed light beam 224 so that it is sent back into the dischargechamber 240. The discharge chamber 240 includes a pair of elongatedelectrodes 241, a gain medium 219 that is a gas mixture, and a fan forcirculating the gas mixture between the electrodes 241.

The output light beam 260 is directed through a bandwidth analysismodule 262, where various parameters (such as the bandwidth or thewavelength) of the beam 260 may be measured. The output light beam 260may also be directed through a beam preparation system 263. The beampreparation system 263 may include, for example, a pulse stretcher,where each of the pulses of the output light beam 260 is stretched intime, for example, in an optical delay unit, to adjust for performanceproperties of the light beam that impinges the lithography exposureapparatus 169. The beam preparation system 263 also may include othercomponents that are able to act upon the beam 260 such as, for example,reflective and/or refractive optical elements (such as, for example,lenses and mirrors), filters, and optical apertures (including automatedshutters).

The photolithography system 200 also includes the control system 250. Inthe implementation shown in FIG. 2A, the control system 250 is connectedto various components of the optical source 205. For example, thecontrol system 250 may control when the optical source 205 emits a pulseof light or a burst of light pulses that includes one or more pulses oflight by sending one or more signals to the optical source 205. Thecontrol system 250 is also connected to the lithography exposureapparatus 169. Thus, the control system 250 also may control the variousaspects of the lithography exposure apparatus 169. For example, thecontrol system 250 may control the exposure of the wafer 170 and thusmay be used to control how electronic features are printed on the wafer170. In some implementations, the control system 250 may control thescanning of the wafer 170 by controlling the motion of the slit 176 inthe x-y plane (FIG. 1B). Moreover, the control system 250 may exchangedata with the metrology system 172 and/or the optical system 175.

The lithography exposure apparatus 169 also may include, for example,temperature control devices (such as air conditioning devices and/orheating devices), and/or power supplies for the various electricalcomponents. The control system 250 also may control these components. Insome implementations, the control system 250 is implemented to includemore than one sub-control system, with at least one sub-control system(a lithography controller) dedicated to controlling aspects of thelithography exposure apparatus 169. In these implementations, thecontrol system 250 may be used to control aspects of the lithographyexposure apparatus 169 instead of, or in addition to, using thelithography controller.

The control system 250 includes an electronic processor 251, anelectronic storage 252, and an I/O interface 253. The electronicprocessor 251 includes one or more processors suitable for the executionof a computer program such as a general or special purposemicroprocessor, and any one or more processors of any kind of digitalcomputer. Generally, an electronic processor receives instructions anddata from a read-only memory, a random access memory, or both. Theelectronic processor 251 may be any type of electronic processor.

The electronic storage 252 may be volatile memory, such as RAM, ornon-volatile memory. In some implementations, and the electronic storage252 includes non-volatile and volatile portions or components. Theelectronic storage 252 may store data and information that is used inthe operation of the control system 250, components of the controlsystem 250, and/or systems controlled by the control system 250. Theinformation may be stored in, for example, a look-up table or adatabase. For example, the electronic storage 252 may store data thatindicates values of various properties of the beam 260 under differentoperating conditions and performance scenarios.

Moreover, the electronic storage 252 may store various recipes orprocess programs 259 that dictate parameters of the light beam 260during use. For example, the electronic storage 252 may store a recipethat indicates the wavelength of each pulse in the light beam 260 for aparticular exposure pass. The recipe may indicate different wavelengthsfor different exposure passes. The wavelength controlling techniquesdiscussed below may be applied on a pulse-by-pulse basis. In otherwords, the wavelength content may be controlled for each individualpulse in an exposure pass to facilitate formation of the aerial imagesat the desired locations along the z axis.

The electronic storage 252 also may store instructions, perhaps as acomputer program, that, when executed, cause the processor 251 tocommunicate with components in the control system 250, the opticalsystem 205, and/or the lithography exposure apparatus 169.

The I/O interface 253 is any kind of electronic interface that allowsthe control system 250 to receive and/or provide data and signals withan operator, the optical system 205, the lithography exposure apparatus169, any component or system within the optical system 205 and/or thelithography exposure apparatus 169, and/or an automated process runningon another electronic device. For example, the I/O interface 253 mayinclude one or more of a visual display, a keyboard, and acommunications interface.

The light beam 260 (and the light beam 160) are pulsed light beams andmay include one or more bursts of pulses that are separated from eachother in time. Each burst may include one or more pulses of light. Insome implementations, a burst includes hundreds of pulses, for example,100-400 pulses. FIGS. 3A-3C provides an overview of the production ofpulses and bursts in the optical source 205. FIG. 3A shows an amplitudeof a wafer exposure signal 300 as a function of time, FIG. 3B shows anamplitude of a gate signal 315 as a function of time, and FIG. 3C showsan amplitude of a trigger signal as a function of time.

The control system 250 may be configured to send the wafer exposuresignal 300 to the optical source 205 to control the optical source 205to produce the light beam 260. In the example shown in FIG. 3A, thewafer exposure signal 300 has a high value 305 (for example, 1) for aperiod of time 307 during which the optical source 205 produces burstsof pulses of light. The wafer exposure signal 300 otherwise has a lowvalue 310 (for example, 0) when the wafer 170 is not being exposed.

Referring to FIG. 3B, the light beam 260 is a pulsed light beam, and thelight beam 260 includes bursts of pulses. The control system 250 alsocontrols the duration and frequency of the bursts of pulses by sending agate signal 315 to the optical source 205. The gate signal 315 has ahigh value 320 (for example, 1) during a burst of pulses and a low value325 (for example, 0) during the time between successive bursts. In theexample shown, the duration of time at which the gate signal 315 has thehigh value is also the duration of a burst 316. The bursts are separatedin time by an inter-burst time interval. During the inter-burst timeinterval, the lithography exposure apparatus 169 may position the nextdie on the wafer 170 for exposure.

Referring to FIG. 3C, the control system 250 also controls therepetition rate of the pulses within each burst with a trigger signal330. The trigger signal 330 includes triggers 340, one of which isprovided to the optical source 205 to cause the optical source 205 toproduce a pulse of light. The control system 250 may send a trigger 340to the source 205 each time a pulse is to be produced. Thus, therepetition rate of the pulses produced by the optical source 205 (thetime between two successive pulses) may be set by the trigger signal330.

As discussed above, when the gain medium 219 is pumped by applyingvoltage to the electrodes 217, the gain medium 219 emits light. Whenvoltage is applied to the electrodes 217 in pulses, the light emittedfrom the medium 219 is also pulsed. Thus, the repetition rate of thepulsed light beam 260 is determined by the rate at which voltage isapplied to the electrodes 217, with each application of voltageproducing a pulse of light. The pulse of light propagates through thegain medium 219 and exits the chamber 214 through the output coupler218. Thus, a train of pulses is created by periodic, repeatedapplication of voltage to the electrodes 217. The trigger signal 330,for example, may be used to control the application of voltage to theelectrodes 217 and the repetition rate of the pulses, which may rangebetween about 500 and 6,000 Hz for most applications. In someimplementations, the repetition rate may be greater than 6,000 Hz, andmay be, for example, 12,000 Hz or greater

The signals from the control system 250 may also be used to control theelectrodes 217, 241 within the master oscillator 212 and the poweramplifier 230, respectively, for controlling the respective pulseenergies of the master oscillator 212 and the power amplifier 230, andthus, the energy of the light beam 260. There may be a delay between thesignal provided to the electrodes 217 and the signal provided to theelectrodes 241. The amount of delay may influence properties of the beam260, such as the amount of coherence in the pulsed light beam 260.

The pulsed light beam 260 may have an average output power in the rangeof tens of watts, for example, from about 50 W to about 130 W. Theirradiance (that is, the average power per unit area) of the light beam260 at the output may range from 60 W/cm² to 80 W/cm².

Referring also to FIG. 4 , the wafer 170 is irradiated by the light beam260. The lithography exposure apparatus 169 includes the optical system175 (FIGS. 1A and 1B). In the example of FIG. 4 , the optical system 175(not shown) includes an illuminator system 429, which includes anobjective arrangement 432. The objective arrangement 432 includes theprojection lens 177 (FIG. 1B) and enables the image transfer to occurfrom the mask 174 to the photoresist on the wafer 170. The illuminatorsystem 429 adjusts the range of angles for the light beam 260 impingingon the mask 174. The illuminator system 429 also may homogenize (makeuniform) the intensity distribution of the light beam 260 in the x-yplane across the mask 174.

In some implementations, an immersion medium may be supplied to coverthe wafer 170. The immersion medium may be a liquid (such as water) forliquid immersion lithography. In other implementations in which thelithography is a dry system, the immersion medium may be a gas such asdry nitrogen, dry air, or clean air. In other implementations, the wafer170 may be exposed within a pressure-controlled environment (such as avacuum or partial vacuum).

During an exposure pass, a plurality of N pulses of the light beam 260illuminates the same area of the wafer 170. N may be any integer numbergreater than one. The number of pulses N of the light beam 110 thatilluminate the same area may be referred to as an exposure window orexposure pass 400. The size of the window 400 may be controlled by theslit 176. For example, the slit 176 may include a plurality of bladesthat are movable such that the blades form an aperture in oneconfiguration and close the aperture in another configuration. Byarranging the blades of the slit 176 to form an aperture of a particularsize, the size of the window 400 also may be controlled.

The N pulses also determine an illumination dose for the exposure pass.The illumination dose is the amount of optical energy that is deliveredto the wafer during the exposure pass. Thus, properties of the N pulses,such as the optical energy in each pulse, determine the illuminationdose. Moreover, and as discussed in greater detail below, the N pulsesalso may be used to determine the amount of light in each of the aerialimages 173 a, 173 b. In particular, a recipe may specify that of the Npulses, a certain number of pulses have a first primary wavelength thatforms the aerial image 173 a and a certain number of pulses have asecond primary wavelength that forms the aerial image 173 b.

Additionally, the slit 176 and/or the mask 174 may move in in a scanningdirection in the x-y plane such that only a portion of the wafer 170 isexposed at a given time or during a particular exposure scan (orexposure pass). The size of the area on the wafer 170 exposed by thelight beam 160 is determined by the distance between the blades in thenon-scanning direction and by the length (distance) of the scan in thescanning direction. In some implementations, the value of N is in thetens, for example, from 10-100 pulses. In other implementations, thevalue of N is greater than 100 pulses, for example, from 100-500 pulses.An exposure field 479 of the wafer 170 is the physical area of the wafer170 that is exposed in one scan of an exposure slit or window within thelithography exposure apparatus 169.

The wafer stage 171, the mask 174, and the objective arrangement 432 arefixed to associated actuation systems to thereby form a scanningarrangement. In the scanning arrangement, one or more of the mask 174,the objective arrangement 432, and the wafer 170 (via the stage 171) maymove relative to each other in the x-y plane. However, aside fromincidental relative operational motion between the wafer stage 171, themask 174, and the objective arrangement 432, these elements are notmoved relative to each other along the z axis during an exposure pass oran exposure pass.

Referring to FIG. 5 , a flow chart of a process 500 is shown. Theprocess 500 is an example of a process for forming a three-dimensionalsemiconductor component or a portion of such a component. The process500 may be performed using the photolithography system 100 or 200. Theprocess 500 is discussed with respect to the system 200 shown in FIG.2A. The process 500 is also discussed with respect to FIGS. 6A-10B.

The light beam 260 is directed toward the mask 174 (510). The light beam260 is a pulsed light beam that includes a plurality of pulses, each ofwhich are separated from each other in time such as shown in FIG. 3C.FIGS. 6A and 6B show examples of optical spectra of a single pulse thatis part of the light beam 260. Other pulses in the light beam 260 mayhave different optical spectra.

Referring to FIG. 6A, an optical spectrum 601A of a pulse of light 600Ais shown. The pulse of light 600A has non-zero intensity within a bandof wavelengths. The band of wavelengths also may be referred to as thebandwidth of the pulse 600A.

The information shown in FIG. 6A is the instantaneous optical spectrum601A (or emission spectrum) of the pulse 600A. The optical spectrum 601Acontains information about how the optical energy or power of a pulse ofthe light beam 260 is distributed over different wavelengths (orfrequencies). The optical spectrum 601A is depicted in the form of adiagram where the spectral intensity (not necessarily with an absolutecalibration) is plotted as a function of the wavelength or opticalfrequency. The optical spectrum 601A may be referred to as the spectralshape or intensity spectrum of a pulse of the light beam 260. The pulse600A has a primary wavelength 602A, which, in the example of FIG. 6A, isthe peak intensity. Although the discussion of the pulses of the lightbeam 260 and the aerial images formed by the pulses of the light beam260 refers to the primary wavelengths of the pulses, the pulses includewavelengths other than the primary wavelength and the pulses have afinite bandwidth that may be characterized by a metric. For example, thefull width of the spectrum 601A at a fraction (X) of the maximum peakintensity of the spectral shape (referred to as FWXM) may be used tocharacterize the light beam bandwidth. As another example, the width ofthe spectrum that contains a fraction (Y) of the integrated spectralintensity (referred to as EY) may be used to characterize the light beambandwidth.

The pulse 600A is shown as an example of a pulse that may be in thelight beam 260. When the pulse 600A is used to expose a portion of thewafer 120, the light in the pulse forms an aerial image. The location ofthe aerial image in the z direction (FIGS. 1C and 4 ) is determined bythe value of the primary wavelength 602A. The various pulses in thelight beam 260 may have different primary wavelengths. For example, togenerate two aerial images during a single exposure pass, some of thepulses of the light beam 260 have one primary wavelength (a firstprimary wavelength) and the other pulse of the light beam 260 haveanother primary wavelength (a second primary wavelength). The first andsecond primary wavelengths are different wavelengths. The wavelengthdifference between the first and second primary wavelengths may bereferred to as the spectral separation. The spectral separation may be,for example, 200 femtometers (fm) to 5 picometers (pm). Although thewavelengths of the various pulses in the light beam 260 may bedifferent, the shape of the optical spectra of the pulses may be thesame.

The light source 205 may dither or switch the primary wavelength betweenthe first and second primary wavelengths on a pulse-to-pulse basis suchthat every pulse has a different primary wavelength than a pulse thatimmediately precedes or follows the pulse in time. In theseimplementations, assuming that all of the pulses in the light beam 260have the same intensity, distributing the first and second primarywavelengths in this manner results in two aerial images at differentlocations in the z direction with the same intensity.

In some implementations, a certain portion (for example, 33%) of thepulses have the first primary wavelength, and the remainder (67% in thisexample) have the second primary wavelength. In these implementations,assuming that all of the pulses in the light beam 260 have the sameintensity, two aerial images are formed of different intensities. Theaerial image formed by the pulses having the first primary wavelengthhas about half of the intensity of the aerial image formed by the pulseshaving the second primary wavelength. In this way, the dose provided toa particular location in the wafer 170 along the z axis may becontrolled by controlling the portion of the N pulses that have each ofthe first and second primary wavelengths.

The portion of pulses that are to have a particular primary wavelengthfor an exposure pass may be specified in a recipe file 259 that isstored on the electronic storage 252. The recipe 259 specifies the ratioof the various primary wavelengths for an exposure pass. The recipe 259also may specify the ratio for other exposure passes, such that adifferent ratio may be used for other exposure passes and the aerialimages may be adjusted or controlled on a field-by-field basis.

Referring to FIG. 6B, an optical spectrum 601B of a pulse 600B is shown.The pulse 600B is another example of a pulse of the light beam 260. Theoptical spectrum 601B of the pulse 600B has a different shape than theoptical spectrum 601A. In particular, the optical spectrum 601B has twopeaks that correspond to two primary wavelengths 602B_1 and 602B_2 ofthe pulse 600B. The pulse 600B is part of the light beam 260. When thepulse 600B is used to expose a portion of the wafer 120, the light inthe pulse forms two aerial images at different locations along the zaxis on the wafer. The locations of the aerial images are determined bythe wavelengths of the primary wavelengths 602B_1 and 602B_2.

The pulses shown in FIGS. 6A and 6B may be formed by any hardwarecapable of forming such pulses. For example, a pulse train of pulsessuch as the pulse 600A may be formed using a line narrowing modulesimilar to the line narrowing module 216C of FIG. 2C. The wavelength ofthe light diffracted by the grating 291 depends on the angle of thelight that is incident on the grating. A mechanism to change the angleof incidence of light that interacts with the grating 291 may be usedwith such a line narrowing module to create a pulse train with N pulsesfor an exposure pass, where at least one of the N pulses has a primarywavelength that is different from the primary wavelength of anotherpulse of the N pulses. For example, one of the prisms 292, 293, 294, 295may be rotated to change the angle of light that is incident on thegrating 291 on a pulse-by-pulse basis. In some implementations, the linenarrowing module includes a mirror that is in the path of the beam 260and is movable to change the angle of light that is incident on thegrating 291. An example of such an implementation is discussed, forexample, in U.S. Pat. No. 6,192,064, titled NARROW BAND LASER WITH FINEWAVELENGTH CONTROL, issued on Feb. 20, 2001.

A pulse such as the pulse 600B (FIG. 6B) also may be formed using a linenarrowing module similar to the line narrowing module 216C of FIG. 2C.For example, a stimulated optical element, such as an acousto-opticmodulator, may be placed in the line narrowing module 216C in the pathof the beam 260. The acousto-optic modulator deflects incident light atan angle that depends on the frequency of an acoustic wave used toexcite the modulator. An acoustic modulator includes a material, such asglass or quartz, that allows acoustic waves to propagate, and atransducer coupled to the material. The transducer vibrates in responseto an excitation signal and the vibrations create acoustic waves in thematerial. The acoustic waves form moving planes of expansion andcompression that change the index of refraction of the material. As aresult, the acoustic waves act as a diffraction grating such thatincident light is diffracted and exits the material at several differentangles simultaneously. Light from two or more of the orders may beallowed to reach the grating 291, and the light in each of the variousdiffraction orders has a different angle of incidence on the grating291. In this way, a single pulse that includes two or more primarywavelengths may be formed. An example of a line narrowing module thatincludes an acousto-optic modulator is discussed, for example, in U.S.Pat. No. 7,154,928, titled LASER OUTPUT BEAM WAVEFRONT SPLITTER FORBANDWIDTH SPECTRUM CONTROL, issued on Dec. 26, 2006.

A set of pulses of light are passed through the mask 174 toward thewafer 170 during a single exposure pass (520). As discussed above, Npulses of light may be provided to the wafer 170 during the exposurepass. The N pulses of light may be consecutive pulses of light in thebeam 260. The exposed portion of the wafer 170 sees an average of theoptical spectrum of each of the N pulses over the exposure pass. Thus,if a portion of the N pulses have a first primary wavelength and theremaining N pulses have a second primary wavelength, the average opticalspectrum at the wafer 170 will be an optical spectrum that includes apeak at the first primary wavelength and a peak at the second primarywavelength. Similarly, if all or some of the individual pulses of the Npulses have more than one primary wavelength, those primary wavelengthsmay form peaks in the average optical spectrum. FIG. 7 shows an exampleof an average optical spectrum 701 at the wafer 170. The averagedoptical spectrum 701 includes a first primary wavelength 702_1 and asecond primary wavelength 702_2. In the example of FIG. 7 , the firstprimary wavelength 702_1 and the second primary wavelength 702_2 areseparated by a spectral separation 703 of about 500 fm however othercombinations can also be considered. The spectral separation 703 is suchthat the first primary wavelength 702_1 and the second primarywavelength 702_2 are distinct, and the average optical spectrum 701includes a spectral region 704 of little to no intensity between thewavelengths 702_1 and 702_2.

Two or more aerial images, for example, the first based on the firstprimary wavelength and the second based on the second primarywavelength, are formed at the wafer 170 based on the average opticalspectrum (530). Continuing the example of the averaged optical spectrum701 and referring also to FIG. 8A, two aerial images 873 a and 873 b areformed in a single exposure pass based on the N pulses. The N pulsesinclude pulses that have the first primary wavelength 702_1 and pulsesthat have the second primary wavelength 702_2. The pulses that have thefirst primary wavelength 702_1 form the first aerial image 873 a, andthe pulses that have the second primary wavelength 702_2 form the secondaerial image 873 b. The aerial image 873 a is formed at a first plane878 a, and the aerial image 873 b is formed at a second plane 878 b. Theplanes 878 a and 878 b are perpendicular to a direction of propagationof the light beam 260 at the wafer 170. The planes 878 a and 878 b areseparated along the z direction by a separation distance 879.

The separation distance 879 is larger than the depth of focus of thelithography apparatus 169 for an averaged optical spectrum that has asingle primary wavelength. The depth of focus may be defined for a dosevalue (an amount of optical energy provided to the wafer) as the rangeof focus along the z direction at which that dose provides a featuresize that is within an acceptable range of feature sizes for the processthat is being applied to the wafer 170. The process 500 is able toincrease the depth of focus of the lithography exposure apparatus 169 byproviding more than one distinct aerial image at the wafer 170 during asingle exposure pass. This is because the plurality of aerial images areeach able to expose the wafer at a different location in the z directionwith features that are within the acceptable range of feature sizes. Inother words, the process 500 is able to provide the lithography exposureapparatus 169 with a greater rage of depth of focus during a singleexposure pass. As discussed above, the operator of the lithographyexposure apparatus 169 may control various parameters of the exposureprocess through the recipe file 259. In some implementations, theoperator of the lithography exposure apparatus 169 may receiveinformation from a simulation program, such as the Tachyon Source-MaskOptimization (SMO) available from Brion, an ASML Company, and thisinformation may be used to program or otherwise specify the parametersof the recipe file 259. For example, the operator of the lithographyexposure apparatus 169 may know that an upcoming lot is not going torequire as much depth of focus as previously exposed lot. In thisexample, the operator may specify a depth of focus and a dose variationto the simulation program, and the simulation program returns the valueof the spectral separation 703 to achieve the desired parameters. Theoperator may then specify the value of the spectral separation 703 forthe upcoming lot by programing the recipe file 259 through the I/Ointerface 253. In some implementations, the operator may use thesimulation to determine whether or not a greater depth of focus (such asis possible by exposing the wafer 170 with a plurality of aerial imagesat distinct planes) is needed for a particular exposure pass. Ininstances in which the greater depth of focus is not required to form aparticular portion of the semiconductor component, the recipe file 259may be structured so that, for example, the exposure pass used to formthat particular portion of the semiconductor component has an averagedoptical spectrum that includes a single primary wavelength.

Moreover, the operator and/or simulator may receive information aboutthe formed three-dimensional component as measured by the metrologysystem 172 or by another sensor. For example, the metrology system 172may provide data relating to a sidewall angle of the formed 3Dsemiconductor component and the data may be used to program parametersin the recipe file 259 for a subsequent exposure pass.

FIG. 8B shows the aerial image 873 a in the x-y plane (looking into thepage in FIG. 8A) at the plane 878 a. The aerial images 873 a and 873 bare generally two-dimensional intensity patterns that are formed in thex-y plane. The nature of the intensity pattern depends on thecharacteristics of the mask 174. The first and second planes 878 a, 878b are portions of the wafer 170. As illustrated in FIG. 8B, the firstplane 878 a may be only a small portion of the entire wafer 170.

The value of the separation distance 879 depends on the spectralseparation 703 and on properties of the optical system 275. For example,the value of the separation distance 879 may depend on the focal length,aberration, and other properties of lenses and other optical elements inthe optical system 275. For a scanner lens with a chromatic aberrationC, the separation distance 879 may be determined from Equation 1:

ΔD=C*Δλ.  Equation (1),

where ΔD is the separation distance 879 in nanometers (nm), C is thechromatic aberration (defined as the distance the focal plane moves inthe propagation direction for a wavelength change), and Δλ, is thespectral separation 873 in picometers. The separation distance 875 maybe, for example, 5000 nm (5 μm), and the spectral separation 873 may beabout 200-300 fm.

Moreover, due to variations in manufacturing and installation processesand/or modifications made by end users, different primary wavelengthsmay be required to achieve a desired separation distance 879 for aparticular instance of a certain type of exposure apparatus 169. Asdiscussed above, a recipe or process control program 259 may be storedon the electronic storage 252 of the control system 250. The recipe 259may be modified or programmed to be customized to a particular exposureapparatus or a type of exposure apparatus. The recipe 259 may beprogrammed when the lithography system 200 is manufactured and/or therecipe 259 may be programmed via, for example, the I/O interface 253, byan end user or other operator familiar with the performance of thesystem 200.

The recipe 259 also may specify a different separation distance 879 fordifferent exposure passes used to expose different areas of the wafer170. Additionally or alternatively, the recipe 259 may specify theseparation distance 879 on a per-lot or per-layer basis or on aper-wafer basis. A lot or a layer is a group of wafers that areprocessed by the same exposure apparatus under the same nominalconditions. The recipe 259 also allows specification of other parametersrelated to the aerial images 873 a, 873 b, such as the dose provided byeach image. For example, the recipe 259 may specify a ratio of thenumber of pulses in the N pulses that have the first primary wavelength702_1 to the number of pulses that have the second primary wavelength702_2. These other parameters also may be specified on a per-field,per-lot (or per-layer), and/or per-wafer basis.

Moreover, the recipe 259 may specify that some layers are not exposedwith the first primary wavelength 702_1 and the second primarywavelength 702_2 and are instead exposed with a pulse that has anoptical spectrum that includes a single primary wavelength. Such anoptical spectrum may be used, for example, when a planar semiconductorcomponent is to be formed instead of a three-dimensional semiconductorcomponent. The I/O interface 253 allows an end-user and/or manufacturerto program or create the recipe to specify the number of primarywavelengths, including a scenario in which a single primary wavelengthis used, for example, for a particular layer or lot.

Additionally, although the example above discusses the average opticalspectrum 701 having two primary wavelengths, in other examples, theaverage optical spectrum 701 may have more than two primary wavelengths(for example, three, four, or five primary wavelengths), each of whichare separated from the nearest other primary wavelength by a spectralseparation and a region such as the region 704. The I/O interface 253allows an end-user and/or manufacturer to program or create the recipeto specify these parameters.

A three-dimensional (3D) semiconductor component is formed (540). FIG.9A shows a cross-sectional view of an example of a 3D semiconductorcomponent 995. FIG. 9B shows the wafer 170 and the component 995 in thex-y plane at the first plane 878 a. The 3D semiconductor component 995may be a complete component or a portion of a larger component. The 3Dsemiconductor component 995 may be any type of semiconductor componentthat has features that are not all formed at one z location in the wafer170. For example, the 3D semiconductor component may be a device thatincludes recesses or openings that extend along the z axis. The 3Dsemiconductor component may be used for any type of electronicapplication. For example, the 3D semiconductor component may be all orpart of a 3D NAND flash memory component. A 3D NAND flash memory is amemory in which memory cells are stacked along the z axis in layers.

In the example of FIG. 9A, the 3D semiconductor component 995 includes arecess 996 that is formed in a periphery 999. The recess 996 includes afloor 997 and a sidewall 998, which extends generally along the z axisbetween the periphery 999 and the floor 997. The floor 997 is formed byexposing photoresist at the plane 878 b with light that is in the secondaerial image 873 b (FIG. 8A). Features on the periphery 999 are formedusing light that is in the first aerial image 873 a (FIG. 8A).

Using the process 500 also may result in a sidewall angle 992 beingequal to 90° or closer to 90° than is possible with other processes. Thesidewall angle 992 is the angle between the floor 997 and the sidewall998. If the sidewall 998 extends in the x-z plane and the floor extendsin the x-y plane, the sidewall angle 992 is 90° and may be consideredvertical in this example. A vertical sidewall angle is desirablebecause, for example, such a sidewall allows for more well-definedfeatures in a 3D semiconductor component. The process 500 achieves asidewall angle 992 that is equal or close to 90° because the locationsof the first aerial image 873 a and the second aerial image 873 b (thefirst plane 878 a and the second plane 878 b, respectively) are separateimages that are in different parts of the wafer 170. Forming separateaerial images in a single exposure pass allows the quality of each ofthe images to be improved resulting in a more defined feature that ismore vertically oriented as compared to a feature formed by a singleaerial of lower quality.

FIGS. 10A and 10B are examples of simulated data relating to the process500. FIG. 10A shows three plots 1001, 1002, 1003 of aerial imageintensity versus mask position along the y axis (FIG. 9A). Each of theplots 1001, 1002, 1003 represents intensity versus mask position for oneaerial image. In FIG. 10A, the plot 1001 represents a simulation of anaverage optical spectrum that forms two aerial images during a singleexposure pass, such as discussed above with respect to FIG. 5 . The plot1002 represents a simulation of a situation in which the wafer stage istilted according to ASML's EFESE technique, which is a procedure forincreasing the depth of focus to facilitate the printing ofthree-dimensional features (such as vias and holes) on a wafer. In theEFESE technique, the wafer stage is tilted at an angle to scan theaerial image through the focus while exposing the wafer. The EFESEtechnique generally results in a greater depth of focus. In FIG. 10A,only the plot 1002 represents data simulated using the EFESE technique.The remaining data shown on FIG. 10A did not employ the EFESE technique.The plot 1003 represents data from a simulation of a best focus based ondose.

The aerial image intensity as a function of mask position shown in FIG.10A illustrates that forming two or more aerial images in a singleexposure pass may produce similar contrast as tilting the wafer stage. Agreater contrast indicates that the three-dimensional features that areat different locations along the z axis (FIG. 8A) are more likely to beproperly formed.

FIG. 10B shows three plots 1004, 1005, 1006 of critical dimension as afunction of the focus position for three different aerial images, witheach aerial image averaged over an exposure pass. In FIG. 10B, the plot10004 represents data from a simulation in which no EFESE technique wasapplied and a single aerial image was formed. The plot 1005 representsdata from a simulation in which the EFESE technique was applied. Asshown, the EFESE technique increases the depth of focus as compared tothe no-EFESE simulation because the critical dimension value remains thesame for a further distance from zero focus. The plot 1005 representsdata from a simulation in which two aerial images were generated in asingle exposure pass and no EFESE technique was employed. The depth offocus for the no-EFESE simulations using multiple aerial images are onpar or better than the EFESE technique. Thus, the process 500 may beused to achieve a greater depth of focus in a single exposure passwithout relying on a technique such as EFESE.

The embodiments may further be described using the following clauses:

1. A method of forming a three-dimensional semiconductor component usinga photolithography system, the method comprising:

directing a pulsed light beam along a direction of propagation toward amask, the pulsed light beam comprising a plurality of pulses of light;

passing a set of the pulses of light in the light beam through the masktoward a wafer during a single exposure pass;

generating, during the single exposure pass, at least a first aerialimage and a second aerial image on the wafer based on pulses of light inthe set of pulses that pass through the mask, the first aerial imagebeing at a first plane on the wafer and the second aerial image being ata second plane on the wafer, the first plane and the second plane beingseparated from each other by a separation distance along the directionof propagation; and

patterning, in photoresist, the three-dimensional semiconductorcomponent based on an interaction between light in the first aerialimage and a material in a first portion of the wafer and an interactionbetween light in the second aerial image and a material in a secondportion of the wafer, wherein

at least one of the pulses in the set of pulses has a first primarywavelength and at least one of the other pulses in the set of pulses hasa second primary wavelength that is different from the first primarywavelength, such that spectra of the first and second set of pulses arespectrally distinct and the separation distance is based on thedifference between the first primary wavelength and the second primarywavelength.

2. The method of clause 1, wherein at least one of the pulses in the setof pulses that passes through the mask during the single exposure passcomprises more than one primary wavelength of light.3. The method of clause 2, wherein each primary wavelength is separatedby a spectral separation of 200 femtometers (fm) to 500 picometers (pm)from the nearest other primary wavelength.4. The method of clause 1, wherein the separation distance between thefirst aerial image and the second aerial image changes during the singleexposure pass.5. The method of clause 1, wherein the single exposure pass is a firstexposure pass, and the method further comprising: passing a second setof pulses of light in the light beam through the mask toward the waferduring a second exposure pass and after the first exposure pass iscompleted, and wherein the separation distance between the first aerialimage and the second aerial image is different during the first exposurepass and the second exposure pass.6. The method of clause 1, wherein the separation distance between thefirst aerial image and the second aerial image is set prior to thesingle exposure pass, and the separation distance does not change duringthe single exposure pass.7. The method of clause 6, wherein the separation distance between thefirst aerial image and the second aerial image is set to accommodate oneor more features of the photolithography system.8. The method of clause 1, wherein the set of pulses comprises a firstgroup of pulses of light and a second group of pulses of light, eachpulse in the first group of pulses of light has the first primarywavelength, each pulse in the second group of pulses has the secondprimary wavelength, and the method further comprising:

controlling a property of the first group of pulses to thereby controlan amount of light in the first aerial image; and

controlling a property of the second group of pulses to thereby controlan amount of light in the second aerial image.

9. The method of clause 8, wherein the property of the first groupcomprises a count of pulses in the first group, and the property of thesecond group comprises a count of pulses in the second group.10. The method of clause 9, wherein controlling the count of pulses inthe first group comprises determining, before the single exposure passbegins, a first number of pulses to include in the first group ofpulses, and controlling the count of pulses in the second group ofpulses comprises determining, before the single exposure pass, a secondnumber of pulses to include in the second group of pulses.11. The method of clause 10, wherein determining the first number ofpulses and the second number of pulses comprises one or more of: (a)receiving input from an operator and (b) accessing a pre-defined settingassociated with the photolithography system.12. The method of clause 8, wherein the property of the first group ofpulses comprises an intensity of each pulse in the first group, and theproperty of the second group of pulses comprises an intensity of eachpulse in the second group.13. The method of clause 1, wherein the first plane on the wafer and thesecond plane on the wafer are planes that are substantiallyperpendicular to the direction of propagation.14. The method of clause 9, wherein the first group of pulses and thesecond group of pulses comprise all of the pulses that pass through themask in the single exposure pass.15. The method of clause 1, wherein

a first feature of the three-dimensional semiconductor is formed at thefirst plane,

a second feature of the three-dimensional semiconductor is formed at thesecond plane, and the first and second features are displaced from eachother by a sidewall that extends substantially parallel to the directionof propagation.

16. The method of clause 1, wherein the three-dimensional semiconductorcomponent comprises a three-dimensional NAND flash memory component.17. The method of clause 1, wherein the first plane corresponds to afirst focal plane and the second plane corresponds to a second focalplane, and the separation distance between the first plane and thesecond plane is based on a difference between one or more wavelengths ina pulse of light that passes through the mask or a difference between awavelengths among discrete pulses in the set of pulses.18. A photolithography system comprising:

a light source;

a lithography scanner apparatus comprising:

a mask positioned to interact with a pulsed light beam from the lightsource, and

a wafer holder; and

a control system coupled to the light source, the control systemconfigured to cause the light source to emit the pulsed light beamtoward the lithography scanner apparatus during a single exposure passsuch that, during the single exposure pass, at least a first aerialimage and a second aerial image are formed on a wafer received at thewafer holder based on pulses of light in a set of pulses of light thatpass through the mask along a direction of propagation, the first aerialimage being at a first plane on the wafer and the second aerial imagebeing at a second plane on the wafer, the first plane and the secondplane being separated from each other by a separation distance along thedirection of propagation, and a three-dimensional semiconductorcomponent is formed based on an interaction between light in the firstaerial image and a material in a first portion of the wafer and aninteraction between light in the second aerial image and a material in asecond portion of the wafer, wherein

at least one of the pulses in the set of pulses has a first primarywavelength,

at least one of the other pulses in the set of pulses has a secondprimary wavelength that is different from the first primary wavelengthsuch that spectra of the first and second set of pulses are spectrallydistinct, and

the separation distance is based on the difference between the firstprimary wavelength and the second primary wavelength.

19. The photolithography system of clause 18, wherein the control systemcomprises a computer-readable storage medium, one or more electronicprocessors coupled to the computer-readable storage medium, and aninput/output interface, and a recipe related to the photolithographysystem is stored on the computer-readable storage medium.20. The photolithography system of clause 19, wherein the recipespecifies the separation distance.21. The photolithography system of clause 20, wherein the recipespecifies the separation distance on a per-wafer or per-lot basis.22. The photolithography system of clause 18, wherein the light sourcecomprises a krypton fluoride (KrF) gain medium or a argon fluoride (ArF)gain medium.

Other implementations are within the scope of the claims.

What is claimed is:
 1. A method of forming a three-dimensionalsemiconductor component using a photolithography system, the methodcomprising: directing a pulsed light beam along a direction ofpropagation toward a mask, the pulsed light beam comprising a pluralityof pulses of light; passing a set of the pulses of light in the lightbeam through the mask toward a wafer during a single exposure pass;generating, during the single exposure pass, at least a first aerialimage and a second aerial image on the wafer based on pulses of light inthe set of pulses that pass through the mask, the first aerial imagebeing at a first plane on the wafer and the second aerial image being ata second plane on the wafer, the first plane and the second plane beingseparated from each other by a separation distance along the directionof propagation; and patterning, in photoresist, the three-dimensionalsemiconductor component based on an interaction between light in thefirst aerial image and a material in a first portion of the wafer and aninteraction between light in the second aerial image and a material in asecond portion of the wafer, wherein at least one of the pulses in theset of pulses has a first primary wavelength and at least one of theother pulses in the set of pulses has a second primary wavelength thatis different from the first primary wavelength, such that spectra of thefirst and second set of pulses are spectrally distinct and theseparation distance is based on the difference between the first primarywavelength and the second primary wavelength.
 2. The method of claim 1,wherein at least one of the pulses in the set of pulses that passesthrough the mask during the single exposure pass comprises more than oneprimary wavelength of light.
 3. The method of claim 2, wherein eachprimary wavelength is separated by a spectral separation of 200femtometers (fm) to 500 picometers (pm) from the nearest other primarywavelength.
 4. The method of claim 1, wherein the separation distancebetween the first aerial image and the second aerial image changesduring the single exposure pass.
 5. The method of claim 1, wherein thesingle exposure pass is a first exposure pass, and the method furthercomprising: passing a second set of pulses of light in the light beamthrough the mask toward the wafer during a second exposure pass andafter the first exposure pass is completed, and wherein the separationdistance between the first aerial image and the second aerial image isdifferent during the first exposure pass and the second exposure pass.6. The method of claim 1, wherein the separation distance between thefirst aerial image and the second aerial image is set prior to thesingle exposure pass, and the separation distance does not change duringthe single exposure pass.
 7. The method of claim 6, wherein theseparation distance between the first aerial image and the second aerialimage is set to accommodate one or more features of the photolithographysystem.
 8. The method of claim 1, wherein the set of pulses comprises afirst group of pulses of light and a second group of pulses of light,each pulse in the first group of pulses of light has the first primarywavelength, each pulse in the second group of pulses has the secondprimary wavelength, and the method further comprising: controlling aproperty of the first group of pulses to thereby control an amount oflight in the first aerial image; and controlling a property of thesecond group of pulses to thereby control an amount of light in thesecond aerial image.
 9. The method of claim 8, wherein the property ofthe first group comprises a count of pulses in the first group, and theproperty of the second group comprises a count of pulses in the secondgroup.
 10. The method of claim 9, wherein controlling the count ofpulses in the first group comprises determining, before the singleexposure pass begins, a first number of pulses to include in the firstgroup of pulses, and controlling the count of pulses in the second groupof pulses comprises determining, before the single exposure pass, asecond number of pulses to include in the second group of pulses. 11.The method of claim 10, wherein determining the first number of pulsesand the second number of pulses comprises one or more of: (a) receivinginput from an operator and (b) accessing a pre-defined settingassociated with the photolithography system.
 12. The method of claim 8,wherein the property of the first group of pulses comprises an intensityof each pulse in the first group, and the property of the second groupof pulses comprises an intensity of each pulse in the second group. 13.The method of claim 1, wherein the first plane on the wafer and thesecond plane on the wafer are planes that are substantiallyperpendicular to the direction of propagation.
 14. The method of claim9, wherein the first group of pulses and the second group of pulsescomprise all of the pulses that pass through the mask in the singleexposure pass.
 15. The method of claim 1, wherein a first feature of thethree-dimensional semiconductor is formed at the first plane, a secondfeature of the three-dimensional semiconductor is formed at the secondplane, and the first and second features are displaced from each otherby a sidewall that extends substantially parallel to the direction ofpropagation.
 16. The method of claim 1, wherein the three-dimensionalsemiconductor component comprises a three-dimensional NAND flash memorycomponent.
 17. The method of claim 1, wherein the first planecorresponds to a first focal plane and the second plane corresponds to asecond focal plane, and the separation distance between the first planeand the second plane is based on a difference between one or morewavelengths in a pulse of light that passes through the mask or adifference between a wavelengths among discrete pulses in the set ofpulses.
 18. A photolithography system comprising: a light source; alithography scanner apparatus comprising: a mask positioned to interactwith a pulsed light beam from the light source, and a wafer holder; anda control system coupled to the light source, the control systemconfigured to cause the light source to emit the pulsed light beamtoward the lithography scanner apparatus during a single exposure passsuch that, during the single exposure pass, at least a first aerialimage and a second aerial image are formed on a wafer received at thewafer holder based on pulses of light in a set of pulses of light thatpass through the mask along a direction of propagation, the first aerialimage being at a first plane on the wafer and the second aerial imagebeing at a second plane on the wafer, the first plane and the secondplane being separated from each other by a separation distance along thedirection of propagation, and a three-dimensional semiconductorcomponent is formed based on an interaction between light in the firstaerial image and a material in a first portion of the wafer and aninteraction between light in the second aerial image and a material in asecond portion of the wafer, wherein at least one of the pulses in theset of pulses has a first primary wavelength, at least one of the otherpulses in the set of pulses has a second primary wavelength that isdifferent from the first primary wavelength such that spectra of thefirst and second set of pulses are spectrally distinct, and theseparation distance is based on the difference between the first primarywavelength and the second primary wavelength.
 19. The photolithographysystem of claim 18, wherein the control system comprises acomputer-readable storage medium, one or more electronic processorscoupled to the computer-readable storage medium, and an input/outputinterface, and a recipe related to the photolithography system is storedon the computer-readable storage medium.
 20. The photolithography systemof claim 19, wherein the recipe specifies the separation distance. 21.The photolithography system of claim 20, wherein the recipe specifiesthe separation distance on a per-wafer or per-lot basis.
 22. Thephotolithography system of claim 18, wherein the light source comprisesa krypton fluoride (KrF) gain medium or a argon fluoride (ArF) gainmedium.
 23. A photolithography system comprising: a pulsed light source;and a communications interface coupled to the light source andconfigured to receive a plurality of signals, wherein: thecommunications interface is configured to provide the signals to one ormore control modules in the pulsed light source; the signals compriseindications of a timing of pulses of light to be emitted by the pulsedlight source; and the signals comprise an indication of a spectralseparation between a first plurality of pulses among the pulses of lightand a second plurality of pulses among the pulses of light.
 24. Thephotolithography system of claim 23, wherein the signals comprise anindication that a single primary wavelength is to be used for a seriesof pulses among the pulses of light.
 25. The photolithography system ofclaim 23, wherein the signals comprise an indication of one or moreprimary wavelengths of the pulses of light.
 26. The photolithographysystem of claim 23, further comprising: the control modules, wherein thecontrol modules are configured to control a first primary wavelength ofthe first plurality of pulses and a second primary wavelength of thesecond plurality of pulses, such that spectra of the first and secondset of pulses are spectrally distinct.
 27. A system comprising: acommunications interface configured to receive a plurality of signals;and a processor coupled to the communications interface, wherein: thecommunications interface is configured to provide the signals, under thecontrol of the processor, to one or more control modules in a pulsedlight source; the signals comprise indications of a timing of pulses oflight to be emitted by the pulsed light source; and the signals comprisean indication of a spectral separation between a first plurality ofpulses among the pulses of light and a second plurality of pulses amongthe pulses of light.
 28. The system of claim 27, wherein the processoris configured to identify, within the signals, the indications of thetiming of pulses and to trigger pulses of light emitted by the pulsedlight source based on the indications of the timing of pulses.
 29. Thesystem of claim 27, wherein the processor is configured to identify,within the signals, the indication of the spectral separation and todither or switch a wavelength of pulses of emitted by the pulsed lightsource based on the indication of the spectral separation.
 30. Thesystem of claim 27, wherein the signals comprise an indication that asingle primary wavelength is to be used for a series of pulses among thepulses of light.
 31. The system of claim 27, wherein the signalscomprise an indication of one or more primary wavelengths of the pulsesof light.
 32. The system of claim 27, further comprising: the controlmodules, wherein the control modules are configured to control a firstprimary wavelength of the first plurality of pulses and a second primarywavelength of the second plurality of pulses, such that spectra of thefirst and second set of pulses are spectrally distinct.